Sometimes, placebo effects can also be harmful, it is what is known as the nocebo effect. According to a large analysis using volunteer data from 12 clinical trials, more than two-thirds of adverse symptoms from covid-19 vaccines were due to them.
The symptoms of covid vaccines can also be due to the nocebo effect, according to a study. EFE/Jeffrey Arguedas
The nocebo effect of the symptoms of anticovid vaccines
The placebo effect is the supposed improvement in a person’s physical or mental health after a treatment with no pharmacological therapeutic benefit, a sugar pill or a syringe filled with serum, and it has an opposite version, the nocebo, which occurs when an individual experiences unpleasant side effects after also receiving this “lie treatment”.
The exact biological, psychological and genetic underpinnings of why they occur -placebo/nocebo effect- are not well understood, although there are theories that point to expectations as the main cause and others maintain that unconscious factors embedded in the doctor-patient relationship automatically lower the volume of symptoms.
To verify its role in covid-19 vaccines, the team from the BIDMC center, associated with the medical school of Harvard (EE.UU.), conducted a meta-analysis of 12 clinical trials.
The objective was to compare the rates of adverse events reported by the participants who received the vaccines with the rates of those who received a placebo injection – without any vaccine. The results are published in JAMA Network Open.
The 12 trials included reports of adverse events from 22,578 placebo recipients and 22,802 vaccine recipients.
nocebo effect, placebo effect
Although the scientists found that significantly more participants who received the vaccine reported adverse events, almost a third of the participants who received the placebo also reported at least one, with headache and fatigue being the most common.
Specifically, Julia W. Haas and her colleagues at the BIDMC found that after the first injection, more than 35% of placebo recipients experienced systemic adverse effects -symptoms that affect the entire body, such as fever-, the pain being headache and fatigue the most common, with 19.6% and 16.7%, respectively, the center reports in a statement.
16% of placebo recipients reported at least one local effect, such as injection site pain, redness, or swelling.
Haas reminds that adverse events after placebo treatment are common in randomized controlled trials.
“Gathering systematic evidence regarding these nocebo responses in vaccine trials is important for COVID-19 vaccination worldwide, especially as concerns about side effects are reported to be a reason for vaccine hesitation.” .
Compared to the placebo group, after the first injection, 46% of vaccine recipients experienced at least one systemic adverse event and two-thirds of them reported at least one local one.
Although this group received a pharmacologically active treatment, some of their adverse events are attributable to the placebo effect – or in this case, nocebo – since many of these effects also occurred in the placebo group, the researchers say.
The analysis suggests that nocebo accounted for 76% of all adverse events in the vaccine group and nearly a quarter of all reported local effects.
After the second dose, adverse effects in the placebo group decreased to 32% for systemic cases and 12% for local effects.
In contrast, participants who received the vaccine reported more side effects, with 61% systemic adverse events and 73% local adverse events.
The researchers calculated that nocebo accounted for nearly 52% of reported side effects after the second dose.
Ted J. Kaptchuk, another of the signatories, explains that “non-specific symptoms such as headache and fatigue – which we have shown to be especially sensitive to nocebo – are among the most common adverse reactions after vaccination in many information leaflets” .
Evidence suggests that this type of information may cause people to mistakenly attribute common everyday sensations as being from the vaccine, or cause anxiety and worry that make people hyper-alert to the bodily sensations of adverse events.
“Medicine is built on trust,” Kaptchuk stresses: “Our findings lead us to suggest that informing the public about the potential for nocebo responses could help reduce concerns about covid vaccination, which could decrease hesitancy.”
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